The present invention relates generally to wireless communication devices, and in particular to a hybrid matrix amplification system and an antenna array of a wireless communication device.
A hybrid matrix amplifier comprises a parallel set of amplifiers whose inputs are fed, and output are combined, by multi-port matrices, made up of hybrid couplers. An exemplary configuration of a hybrid matrix amplifier wherein the matrices are Fourier Transform Matrices (FTMs) is described in U.S. patent application Ser. No. 5,834,972, which patent is assigned to the assignee of the present invention and is hereby incorporated by reference herein in its entirety. In general, a signal applied to an input port of an input FTM is distributed equally among multiple output ports of the FTM. Each signal output by the FTM is then routed to a separate amplifier, where the signal is amplified and then routed to one of multiple input ports of an output FTM. Each signal received at an input port of the output FTM is then distributed among multiple output ports of the output FTM.
Use of a transmitter that includes a hybrid matrix amplifier has been proposed for a base station subsystem (BSS) that service multiple cell sectors and that include multiple adaptive antenna arrays, wherein each antenna array of the multiple antenna arrays provides service to a different sector of the multiple cell sectors. In such a BSS, each signal produced at one of the multiple output ports of an output FTM is routed to an antenna element in an antenna array. Furthermore, each antenna element receiving an FTM output signal is in a different antenna array than the other antenna elements receiving output signals from the FTM.
For example, suppose a BSS services a cell that is divided into four sectors. The BSS includes four antenna arrays, wherein each array includes four antenna elements and services one of the four cell sectors. The BSS further includes four transmit branches. Each transmit branch includes an input FTM having four input and four output ports, an output FTM having four input and four output ports, and an amplifier section comprising four amplifiers, wherein each amplifier of the four amplifiers is operably coupled to an output port of the input FTM and to an input port of the output FTM. Furthermore, each output port of a transmit branch""s output FTM is operably coupled to an antenna element in an antenna array different from the elements and arrays to which the other FTM output ports are coupled. That is, a first output port of the FTM is operably coupled to an element in a first antenna array of the four antenna arrays, a second output port is operably coupled to an element in a second array of the four arrays, a third output port is operably coupled to an element in a third array of the four arrays, and a fourth output port is operably coupled to an element in a fourth array of the four arrays. As a result, each transmit branch is operably coupled to an antenna element in each of the antenna arrays.
Due to variations in length of transmit branch connecting cables, component aging, and variations in component performance, a gain and phase of signals propagating through a transmit branch may vary slowly with time. When each of multiple signals input into a transmit branch and output to a different antenna element than other input signals experiences a different gain and phase than the other input signals, there exists a possibility of cross-sector signal leakage. Cross-sector signal leakage results in a signal intended for transmission in one cell sector interfering with a signal transmitted in another cell sector. Furthermore, when a gain and phase of a signal propagation path through a transmit branch and a coupled antenna element is unknown, uncalibrated, or subject to variation over time, there exists the possibility of improper beam formation when beam forming weights are applied to the elements of the array that includes the coupled element. Therefore a need exists for a method and apparatus of calibrating, or providing error compensation for, signal propagation paths of transmit branches that include hybrid matrix amplifiers, and particularly which calibration or error compensation can be determined without shutting down the BSS.